In recent years, organic EL displays using electroluminescence (EL) of an organic material have been attracting attention as a type of next-generation flat panel display replacing liquid crystal displays.
Unlike the voltage-driven liquid crystal display, the organic EL display is a current-driven display device. Accordingly, there is an urgent need for development of a thin-film transistor (TFT) having excellent characteristics as a driving circuit for the active-matrix display device. The thin-film transistor is used as a switching element for selecting a pixel, a driving transistor for driving a pixel, or others.
For example, a conventional thin-film transistor and a method for manufacturing the thin-film transistor are disclosed in Patent Literature (PTL) 1 and PTL 2. According to the PTL 1 and PTL 2, the thin-film transistor is manufactured by successively stacking thin films on the substrate. In order to improve the turn-on characteristics, it is known to crystallize a semiconductor film into a polycrystalline film by irradiating, with a laser, the semiconductor film which is to serve as a channel region.